Understandings

Variable, Function, and Program

• Variable is the container of data.
• Function is the container of instructions.
• Program is the honestest way to instruct computers. It describes how states are manipulated, and how instructions are carried out.

Memory: Stack and Heap

Stack is a segment of memory that is used to store local variables and function call information of one thread. A new stack frame (a contiguous chunk of memory) is created (push) each time a function is called, and destroyed (pop) when returns. Values live on the stack become invalid when its stack frame is destroyed.

Heap is a pool of memory used for dynamic memory allocation. It allows us to allocate a block of memory of a given size and get a pointer to it, the allocated memory stays reserved until it is explicitly deallocated. Values live on the heap are valid until deallocated. The heap is shared among all threads.